D. Lascar et S. Shelah, UNCOUNTABLE SATURATED STRUCTURES HAVE THE SMALL INDEX PROPERTY, Bulletin of the London Mathematical Society, 25, 1993, pp. 125-131
We prove the following theorem. Let M be a, uncountable saturated stru
cture of cardinality lambda = lambda<lambda and assume that G is a sub
group of Aut (M) whose index is less than or equal to lambda. Then the
re exists a subset A of cardinality strictly less than lambda such tha
t every automorphism of M leaving A pointwise fixed is in G.